This invention is a device for accessing a ROM unit with groups of memory module information of memory modules saved therein, and more particularly having a Mask ROM unit to replace an EEPROM unit in prior art.
Please refer to FIG. 1. A DRAM module is basically constructed by a combination of a Memory Module IC 1 and a DRAM unit 2. The DRAM unit 2 is used to save data, as we have well known. And the Memory Module IC 1 is used to store the information like cell-speed, cell-type, number and size of cells, and other module information of the DRAM unit 2 so as to offer status data of the DRAM unit 2 for a computer system. And, of course, different DRAM modules need to save different information into the Memory Module IC 1. In prior art, an EEPROM is mostly served as this Memory Module IC 1 and, according to the DRAM unit it adapted to, specialized memory module information is imported by DRAM Modules producers.
Please refer to FIG. 2. An EEPROM 12 is arranged. A WP Pin (Write Protect Pin) of the EEPROM 12 connects with a resister 11 and electrically to the GND. This circuit is therefore designed to control the read/write actions of the EEPROM 12.
However, several disadvantages are caused by using an EEPROM as the Memory Module IC, which are:
1, EEPROM is expensive.
2, To Input the Memory Module Information are time cost.
3, The data inputting process may have errors.
4, EEPROM may lose data by effects of surrounding or miss operations of users .
The object of this invention is to resolve said disadvantages. The invention replaces the EEPROM in prior art by a ROM unit (such as a Mask ROM) . Groups of memory module information are pre-formed in the Mask ROM and been selectable for different DRAM memory modules. By having a Mask ROM as the memory module IC, the cost will be reduced because Mask ROM is generally cheaper than EEPROM. The data inputting process can also be omitted and therefore avoid any errors caused during it. And at last, data saved in a Mask ROM will not easily lose by surrounding effects and is unable to change by any users. So, this replacement will overcome said disadvantages of the prior art.
So, this invention is a device for accessing a ROM unit with groups of module information of different memory modules saved therein. The device comprises a selecting circuit which, according to an outer signal, generates a selecting signal, and a decoding circuit which decodes the selecting signal, and a ROM array which saves plural groups of memory module information, and finally a control circuit which operates reading procedure of said memory module information from ROM unit.
In an embodiment, a divider circuit is designed in said selecting circuit. By changing resisters of said divider circuit, corresponded voltages will be read by a comparer, which includes several OP amplifiers, to generate the selecting signal. The selecting signal will thereafter be transferred to the decoding circuit.
In another embodiment, an A/D Converter is applied to replace the comparer. The value of the corresponded voltage will be transformed into a digital signal, which serves as the selecting signal, and then to the decoder circuit .
In another embodiment, multiplexers and fuse disconnecting technique is applied to select the memory module information without changing IC Pin Design. The multiplexers lead signals from the IC pins to two channels: the first output terminals and the second output terminals. Each of the first terminals connects to a fuse and to the decoder circuit. The second terminal connects to the control circuit in the other hand. To disconnect a fuse, a disconnection high voltage (compared to normal voltage) is supplied from the pin(s) of the IC. And another high voltage is applied to a control pin and to a voltage decline circuit inside the IC. The voltage decline circuit operates the multiplexers"" control terminals to have the multiplexers switched their output tunnels from the second output terminals to the first output terminals. At this moment, the disconnection high voltage from the pin(s) is applied to the fuse(s), which is connected with the first output terminals and planed to be disconnected. After said motion, the status of these fuses will be explained by the decoder circuit as an address signal for the ROM unit.
After disconnection, the multiplexers turn their output back to the second terminal which become normal control lines for the control circuit.
However, a switch system is set between the voltage decline circuit and the control circuit which will turn off, when the voltage from the voltage decline circuit is too high to damage the control circuit.